Re: Vestigial Arms

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Mike Taylor wrote:

> Even assuming a fully endothermic tyrannosaur, and even assuming that
> a hadrosaur with a rex-sized lump bitten out of it can keep moving for
> fifteen days, I'm not so sure the hunter couldn't wait it out.  The
> time an animal can go without eating scales with body mass to some
> power (< 1 but > 0!) so that mice and shrews need to eat pretty much
> constantly, but lions can comfortably fast for days.  Come to that, a
> healthy human can fast for fifteen days with no real ill effects.

> Does anyone have figures for fasting durations of extant endothermic
> predators?

I'm a little intimidated about jumping into the conversation here, since
I'm new, but I'll do it anyway. :)

Gregory S Paul's 1988 book _Predatory Dinosaurs of the World_ gives the
following equation for food consumption in endothermic predators
(Appendix A):

F = 0.11(W)^0.75

where F is kg of wet meat needed per day and W is mass in kg.

Of course, there's a lot of debate about the mass of a typical
tyrannosaur, but it's pretty safe to say most estimates fall between
4000 kg and 10 000 kg. That gives F = 55 to 110 kg/d. So if we're
talking about a 500-kg hadrosaur, and assume that the rex could consume
about 85% of the carcass, that would supply her with enough energy for
about 4 to 8 days (and probably make a stalking of more than maybe a day
or 2 not worth it for the next meal).

Paul also writes the following:

'... On average, an 8-tonne _Tyrannosaurus rex_ must bolt down 93 kg of
meat per day, or some 2000 tonnes in a sixty-year life, equal to the
weight of a World War II destroyer! It is also the equivalent of nearly
three thousand cattle, each of which could be eaten in a few bites.
Since _T. rex_ had a uniquely strong skull, it could consume more of a
carcass than most theropods--perhaps 85 percent. So about four hundred
6-tonne _Triceratops_ would feed a _T. rex_ over its life. When _T. rex_
killed a _Triceratops_, it took a few days to eat it, and then it had
enough energy for fifty-five days. It is more likely that six
tyrannosaurs organized to kill nd eat the herbivore. Since each could
take in _two tons_ of meat at a sitting, they ould leave the carcass a
little hungry, but with some eight days' worth of calories on hand.'

And lastly, he says that the equation for ectotherms can be obtained by
dividing the endotherm equation by somewhere between 7 and 10. So for an
ectothermic tyrannosaur (not a workable model, in my view, but that's
another matter), that hadrosaur would sate her for 28 to 80 days,
depending on her mass (assuming an even 8 tonnes, that would narrow the
field down to about 32 to 46 days). Factoring out all the time she
probably spent sleeping, that would make a vigil of up to 2 weeks not
unimaginable.

Any of that helpful at all?

--Sean

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